Conventionally, when a heat sink is attached for cooling an electronic component (power semiconductor element) such as a CPU (central processing unit) or a power transistor which intensely generates heat, application of thermal grease has been widely performed in order to enhance thermal conductivity by filling the thermal grease into a small gap in the joining portion between the electric component and the heat sink. Since the thermal conductivity of the thermal grease is much lower than that of metal, a radiation-fin-integrated semiconductor device in which heat radiation fins and a metallic base plate of a power semiconductor element are integrated has been also realized in order to obtain higher heat radiation performance without using the thermal grease. In the radiation-fin-integrated power semiconductor device, grooves for joining the heat radiation fins into the base plate are provided and resin-molding is performed in a state such that a part of the base plate surface including a portion where the grooves are formed is exposed. The heat radiation fins are inserted into the grooves of the base plate and then swaged to fix them, thereby integrating the base plate and the heat radiation fins to improve the heat radiation performance.
In the power semiconductor device in which the heat radiation performance is improved by the method described above, it is known that noise radiated from the power semiconductor element or malfunction is suppressed by stacking a metal member onto the base plate and by giving the metal member a function to connect the power semiconductor device to the earth potential (refer to Patent Document 1).